Speaker Isolation
Q. Like many other apartment dwellers who own hi-fi equipment, I have a little difficulty from time to time with my neighbors.
Their main complaint seems to be that the bass notes "come through the ceiling." Do you have any suggestions other than turning down the volume and bass controls?
P. SMALLER; New York, N.Y.
A. First, it will be helpful to understand the nature of the problem before working on the solution. In general, high-frequency sound waves are reflected by hard surfaces and absorbed by soft ones. However, low-frequency sound waves tend to pass through wall panels and floorboards almost as though they weren't there. A substantial thickness several feet) of sound-absorbent material is added to absorb (rather than to reflect or pass on) frequencies below 100 Hz or so. In addition, the low-frequency energy usually couples to room surfaces or structural members, and these then serve, directly or in directly, as transmission paths to adjacent rooms or apartments. There are three ways aside from your developing an interest in compositions for the solo flute-to get around these problems of acoustical transmission.
Since acoustic tile or cork paneling will not stop the lows, what will? One effective (if somewhat impractical) technique would be to cover your listening-room floor with an inch or two of sand followed by new flooring resting only on the sand (if the new floor is in direct contact with the old floor or the walls, much of the isolation will be lost). The sand would provide decoupling of the bass through inertial and frictional loss. In other words, it would kill the vibration. A layer of tar or concrete an inch or so thick would also be quite effective, but before embarking on such a project make sure that the floor support beams are adequate for the load.
A more practical approach to the bass-transmission problem is to place the speaker on a compliant pad of some sort. A section of 2 inch (or thicker) foam should work well, assuming that it is not compressed excessively by the weight of the cabinet. If you want to get fancier, you might try putting together the foam-sandwich assembly shown in the accompanying sketch. Vibration tends to get decoupled at the interfaces of disparate materials such as the wood and foam layers shown. This is in addition to the transmission losses in the foam itself. Make sure that the 1/4-inch-thick decorative plinth (A) does not touch panel (B) or the floor. The parts labeled (B) and (C) are 3/4-inch plywood, and the foam is an inch or so thick.
Although an isolating base will do much to inhibit speaker-to-room-structure (floor or shelf) vibration transmission, it won't do any thing about radiated acoustic energy. That is not usually the main problem, however. Note that if the bass reproduction in a particular room .is unduly dependent on the coupling of the speaker cabinet's- vibration to floor or walls, there may be a slight loss of low-end energy. However, if a permanent peace with nearby neighbors is achieved, that seems to be a small price to pay.
A while back (March, 1975) when I answered a question on studio sound proofing I included some material that may provide additional help to audiophiles with neighbor problems. For a free copy, send a stamped, self-addressed long envelope to: STEREO REVIEW, Dept. SP, One Park Ave., New York, NY. 10016.
Philosophical Fidelity
Q. With reference to the comment by Stephen Luzader in a recent issue . . no matter how good a sound system may be, what emanates from it will not be like real live music." I disagree most soundly.
First, music is experiential and need not be "live" to be real any more than a painting is no longer alive after being recorded on canvas.
Secondly, I will put my home sound system with Advent cassettes up against "live" any time, and all but the most obtuse would be more than pleased with the totality of the mu sic that is produced. A $4,000 system is not required; mine cost less than $1,500, which seems to be about the absolute minimum expenditure to achieve adequate "live" sound reproduction.
JERARD W. THORNTON JR., Brownsville, Tex.
A. Far be it from me to put down hi-fi reproduction--or the attempt to achieve it at a reasonable cost--but Mr. Thornton appears to be confused on the semantic level. Let's start with a basic conceptual definition. It seems safe to say that the essential goal of high-fidelity reproduction, expressed as simply as possible, is to make recorded (or transmitted) music sound as- though it were being heard live. If that is the goal (and it seems to me it must be), it then becomes valid to criticize an audio system, including the program material, on the basis of how well that goal is achieved.
Mr. Thornton states (1) that anything that exists is "real" and (2) that he gets an enormous amount of pleasure out of listening to his components. Who can argue with either of those propositions? However, they have nothing to do with the case. For example, I'm sure the scores of the compositions Mr. Thornton listens to are available. And it is likely that someone out there derives just as much pleasure from hearing the music in his mind's ear simply from reading the score as Mr. Thornton gets from listening to his system. No one would deny that the musical score is real, but, on the other hand, no one would confuse that score with the "real live music" either.
My general point is that everyone is entitled to enjoy his music in any way he likes with any kind of equipment (or no equipment at all), but once the term "high fidelity" is invoked, then certain agreed-upon-if ill defined-criteria must be met. In practice, high-fidelity is not an absolute term, for there ate obviously varying degrees of success in the simulation of reality. But the illusion of sonic reality is the goal. And if, with my eyes closed, I can't tell whether I'm listening to live or reproduced sound, that's high fidelity!
-------- The exact dimensions of the parts making up the isolating
base depend upon the size of the speaker. It is best to set up the foam and
panels (B) and (C) before cutting the pieces for plinth (A). The edges of
(A) should not touch the floor or shelf mounting surface.
Automotive Rear Channel
Q. I understand that there was an article in Car and Driver magazine that told how to set up four-channel sound in a car that had a stereo FM radio. Do you know anything about it?
H. A. STANLEY; Chicago, Ill.
A. I do, since was the one who suggested the hookup to C & D after having already installed it in my car several years ago. It occurred to me that my stereo FM radio could provide a synthesized rear-channel using the stereo "difference signal" if I simply ran a pair of wires connected across the two "hot" leads from the front stereo speakers to a separate speaker installed in the rear deck. I wired in the rear speaker, and the results were consistently more impressive than one normally experiences with a difference-signal setup in a home system. This shouldn't have surprised me since, in respect to directionality, stereo itself is also usually more effective in a car than at home.
The wiring for the rear-speaker connections can be tapped in anywhere on the "hot" (usually red) leads going to the right and left front speakers. Most car stereo units will have a plug-in setup for loudspeaker connections.
The sound enhancement achieved by the hookup operates, of course, both for stereo broadcasts and tapes. I have found that "live" recordings such as those of Peter Frampton or Joni Mitchell are particularly impressive since much of the audience reaction seems to come only from the rear speaker, putting the listener right in the center of things. And with large symphonic works, the hall reverberation is reproduced in a surprisingly satisfying way.
The necessary connections are shown in the accompanying diagram. Make sure to use only the two hot leads from the radio/tape player, and avoid grounding either of the leads going to the rear speaker. (Do not use a speaker that has a terminal grounded to its frame). The setup sounds best if the rear speaker plays at the correct relative volume in respect to the front units. You can help en sure this by using an efficient heavy-magnet speaker for the rear. If the sound from the rear is too loud, you can install a 25- or 50-ohm wirewound control (R1) as shown. In my setup, it wasn't necessary.
Because the number of questions we receive each month is greater than we can reply to individually, only those letters selected for use in this column can be answered. Sorry!
Also see:
TAPE HORIZONS: Mixer Basics
Source: Stereo Review (USA magazine)